Correcting inaccurate background mortality in excess hazard models through breakpoints
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(2020) 20:268
TECHNICAL ADVANCE
Open Access
Correcting inaccurate background mortality in excess hazard models through breakpoints Robert Darlin Mba1* , Juste Aristide Goungounga1, Nathalie Grafféo1,2, Roch Giorgi3 and CENSUR working survival group
Abstract Background: Methods for estimating relative survival are widely used in population-based cancer survival studies. These methods are based on splitting the observed (the overall) mortality into excess mortality (due to cancer) and background mortality (due to other causes, as expected in the general population). The latter is derived from life tables usually stratified by age, sex, and calendar year but not by other covariates (such as the deprivation level or the socioeconomic status) which may lack though they would influence background mortality. The absence of these covariates leads to inaccurate background mortality, thus to biases in estimating the excess mortality. These biases may be avoided by adjusting the background mortality for these covariates whenever available. Methods: In this work, we propose a regression model of excess mortality that corrects for potentially inaccurate background mortality by introducing age-dependent multiplicative parameters through breakpoints, which gives some flexibility. The performance of this model was first assessed with a single and two breakpoints in an intensive simulation study, then the method was applied to French population-based data on colorectal cancer. Results: The proposed model proved to be interesting in the simulations and the applications to real data; it limited the bias in parameter estimates of the excess mortality in several scenarios and improved the results and the generalizability of Touraine’s proportional hazards model. Conclusion: Finally, the proposed model is a good approach to correct reliably inaccurate background mortality by introducing multiplicative parameters that depend on age and on an additional variable through breakpoints. Keywords: Excess mortality, Background mortality, Net survival, Additional variable, Breakpoint, Life table, Cancer
Background Many medical research works dedicated to prognosis or to the impact of some covariates on a given disease outcome rely largely on population-based indicators. In cancer epidemiology, using observational data from cancer registry, survival after cancer diagnosis is the most * Correspondence: [email protected] 1 Aix Marseille Univ, Inserm, IRD, SESSTIM, Sciences Économiques & Sociales de la Santé & Traitement de l’Information Médicale, 27 Boulevard Jean Moulin, 13005 Marseille, France Full list of author information is available at the end of the article
widely used indicator but there are now several aspects of survival. Among these aspects, net survival is especially interesting because it provides the survival that would be observed if only deaths from cancer were considered [1]; it eliminates the part of mortality due to other causes and allows then fair comparisons between populations or periods [2]. Unfortunately, in can
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